Microbiological characterization of vegetables and their rhizosphere soil in Eastern Poland

Abstract

The aim of this study was to investigate the bacteriological quality of 5 kinds of vegetables (lettuce, dill, radish, beetroot, carrot) and their rhizosphere soil, originating from conventional farms located in the Lublin Province of Eastern Poland. A total number of 35 samples of fresh vegetables (FV) taken immediately from soil, 35 samples of soil from rhizosphere of these vegetables (SR) and 35 samples of vegetables sold at retail in the markets in Lublin (VR) were examined. The samples were analysed for the content of: aerobic mesophilic bacteria (AMB) grown at 30 °C and 37 °C, Gram-negative bacteria of Enterobacteriaceae family, faecal coliform (FC) bacteria, Salmonella spp., and Clostridium perfringens. Median AMB values determined at 30 °C for FV, SR and VR were 5.27, 5.00, and 5.00 log10 CFU g-1, respectively, being significantly greater compared to those recorded at 37 °C. The exceeding of the threshold value of 6.0 log10 CFU g-1 proposed by Gelosa (1998) was noted only in 5 FV samples grown at 30 °C (14.3%), and in 3 FV samples grown at 37 °C (8.6%). The threshold value was never exceeded in SR and VR samples. Median concentrations of Enterobacteriaceae determined for FV, SR and VR were 4.03, 3.87, and 3.04 log10 CFU g-1, respectively. Eleven species of Enterobacteriaceae were identified in the FV, SR and VR samples. The percent of samples containing Escherichia coli was greatest for VR (22.9%), smaller for FV (17.1%) and smallest for SR (5.7%). The median concentrations of the faecal coliform bacteria (FC), determined by culture at 44 °C, were low, amounting to 1.000 log10 CFU g-1 for FV and SR and 0.00 for VR. All examined vegetable and soil samples tested negative for the presence of Salmonella. The median concentrations of Clostridium perfringens were low, amounting to 0.00 log10 CFU g-1 for all categories of samples. This bacterium was relatively common in soil samples with the prevalence of 40.0%, but very rare in vegetable samples (occurring in 5.7% of FV and in none of VR samples). In conclusion, the results of the present study generally indicate that the microbiological quality of Polish vegetables grown on conventional farms is satisfactory and safe for consumers.